Screws to DIN Standards: Types and Norms Overview

A request to a new supplier specifies "screws DIN 912, M8x20." The quote that comes back lists ISO 4762 instead. To a buyer, that looks like a deviation, but it's actually the same part. Anyone sourcing screws needs to know the common DIN standards and how they relate to current ISO designations. Otherwise, specification mismatches and unnecessary back-and-forth during ordering are likely.

In brief: DIN standards for screws classify head shape, drive type, and thread form. The most common are DIN 933 and 931 (hex head), DIN 912, 7991, 7984, and 6912 (hex socket), and DIN 571 and 84 (wood screw, slotted). Many DIN numbers have been formally replaced by ISO standards, but remain in everyday use as trade names.

What does the DIN number on a screw actually specify?

A screw's DIN number fixes its head shape, drive type, thread profile, and usually its permitted tolerances as well. Two screws sharing the same DIN number are dimensionally and mechanically interchangeable regardless of manufacturer, which is the entire point of standardization.

For procurement, that means a DIN number on a spec sheet replaces a multi-page drawing. That only works if both sides, buyer and supplier, mean the same standard, and not an outdated or informally modified version of it. Especially on orders crossing borders, a quick check on which exact standard the supplier actually manufactures to pays for itself.

Which DIN screw standards come up most often?

The table below lists the DIN screw standards most frequently requested in practice, sorted by head and drive type.

What's the difference between DIN 933 and DIN 931 hex bolts?

These hex head screws (also called hex bolts in English) differ in the shank: DIN 933 has thread running all the way to the head, while DIN 931 has a smooth shank section below the head instead. That distinction matters once a joint relies on a defined, thread-free shank diameter, for instance under shear load perpendicular to the bolt axis.

For short clamping lengths, this difference often makes little practical difference, which is why DIN 933, as the fully threaded variant, is by far the more frequently requested standard. For longer bolts with defined fit requirements in the shank section, DIN 931 remains the correct choice.

Which DIN standards apply to hex socket screws?

Hex socket screws (commonly called Allen or socket screws) cover different installation-space and appearance requirements across four common DIN standards. DIN 912 with a full cylindrical head is the default for general machinery. DIN 7991 with a countersunk head is chosen when the screw needs to sit flush with the surface, for example on visible components or moving parts where a protruding head would interfere.

DIN 7984 and DIN 6912 are both reduced-head-height variants for particularly shallow installation spaces. The practical difference lies in the collar below the hex socket: DIN 6912 offers a somewhat larger bearing surface than DIN 7984 at a comparable overall height.

Which DIN standard applies to slotted or Torx screws?

DIN 84 describes the classic cylindrical-head screw with a slotted drive, still found mainly in older assemblies and light-duty applications today. For Torx drives, no standalone classic DIN number exists in the same sense as for hex or hex socket heads. Torx versions are instead usually offered as a drive variant of existing ISO or DIN head shapes, for example a Torx variant of a cylindrical screw to ISO 4762 (formerly DIN 912). A request should therefore always specify the desired drive explicitly, alongside the head shape.

DIN 603 occupies a special place: the round-head screw with a square neck. It has no tool drive on the head at all, instead a square section below the head keeps the screw from turning while the nut is tightened. This principle is typical for wood and sheet-metal joints in furniture and agricultural machinery, where a tool socket on the head side wouldn't even be accessible.

How do DIN standards relate to current ISO standards?

Most classic DIN screw standards were formally replaced by ISO standards as part of international harmonization. The DIN designation nonetheless remains in everyday use as an established trade name, which is why both numbers still circulate side by side.

In our sourcing projects in the Far East, we regularly see manufacturers list either the old DIN or the new ISO number on drawings and quotes, sometimes even within the same production line. A quick cross-check of both designations at incoming goods inspection prevents misunderstandings, especially for wrench sizes that changed between the DIN and ISO versions.

How do you choose the right screw standard for procurement?

Four criteria determine the right standard: available installation space, the required appearance of the visible surface, tooling availability at the manufacturer, and the required strength class. Tight installation spaces call for hex socket variants with reduced head height, while visible assemblies favor countersunk screws.

The exact tightening torque of a bolted joint doesn't depend on the DIN number alone, but also on strength class, thread size, and the surface's friction coefficient. The systematic calculation for that is provided by VDI guideline 2230 on highly stressed bolted joints. Matching the chosen screw standard, thread tolerances and thread types are also relevant, since they define how precisely internal and external threads need to mesh.

Where no separate tolerance is specified on the drawing, general tolerances per ISO 2768 apply. For the fit between the screw and the bore in the component itself, the H7 fit is often the additional reference value.

On top of that, form and position tolerances define how precisely the geometric position of the tapped hole itself must be held. An overview of the international standardization work itself is provided by the International Organization for Standardization (ISO), and Germany's central authority for national standards remains the German Institute for Standardization (DIN).

Frequently Asked Questions

What does DIN 933 mean for screws?

DIN 933 describes a hex bolt with thread running all the way to the head, with no smooth shank section. It has been formally replaced by ISO 4017, but the DIN designation remains in common use as a trade name.

What does DIN 912 mean for screws?

DIN 912 describes a cylindrical-head screw with a hex socket drive, the most common hex socket standard in general machinery. It has been formally replaced by ISO 4762.

What does DIN 931 mean for screws?

DIN 931 describes a hex bolt with a defined, thread-free shank section below the head, unlike the fully threaded DIN 933. It has been formally replaced by ISO 4014.

Which DIN standard do Torx screws have?

There's no standalone classic DIN number for Torx. Torx is usually offered as a drive variant of existing head shapes such as DIN 912, respectively ISO 4762, and should be specified separately in any request.

Which DIN standard should I reference in a supplier request?

Reference the DIN number along with the current ISO designation, where one exists. That avoids misunderstandings with suppliers who have already switched internally to the ISO version.

Conclusion: the right DIN standard secures smooth screw procurement

Knowing the head shape, drive type, and current ISO equivalent of a DIN screw standard prevents back-and-forth queries and mis-shipments during procurement. The standard family isn't an academic detail, it's the foundation of every precise request to a supplier.

Line Up supports you in sourcing screws and standard fasteners to DIN and ISO standards from reliable Far East manufacturing, including cross-checking the correct standard designation with the manufacturer. 👉 Schedule a no-obligation consultation.